The present invention relates to a display device particularly to a display device and such as a liquid crystal display device which is equipped with a polarized light separator, such as a polarizer or a reflective polarizer, and which can serve as both a reflective type device that displays by reflecting external light and a transmissive type device that displays by allowing light from a light source to be transmitted and, further, to an electronic apparatus such as a portable telephone and a watch using such a display device.
Conventionally, in the case of a reflective type device, which displays by using external light, the display becomes rather hard to see in a dark place as the quantity of light decreases. On the other hand, in the case of a transmissive type device, which displays by using a light source, such as a backlight, the power consumption is rather large due to the light source regardless of whether the device is used in a light place or a dark place. In particular, it is not suitable for a portable display device or the like of the type which is operated by a battery. In view of this, a transflective display device, which can serve as both a reflective type and a transmissive type device, effects reflective type display, mainly in a light place, by controlling the quantity of light emitted from the display screen for each pixel by means of optical elements, such as liquid crystal and a polarized light separator arranged in the optical path thereof while reflecting external light entering from the display screen by a transflective film provided in the device. On the other hand, it effects transmissive type display, mainly in a dark place, by controlling the quantity of light emitted from the display screen for each pixel by means of the above-mentioned optical elements such as liquid crystal and the polarized light separator while applying light from a built-in light source, such as backlight, from behind the above-mentioned transflective film.
A liquid crystal display device which is thus capable of being used as both a reflective type and a transmissive type device and which utilizes a variable transmission polarization axis optical element that rotates the polarization axis of transmission light of a conventional TN (Twisted Nematic) liquid crystal or STN (Super-Twisted Nematic), adopts a construction in which this variable transmission polarization axis optical element is placed between two polarizers.
In the case of the above-described reflective type display, in the construction equipped with these two polarizers, when external light impinges upon the display screen, only a polarized light component in a specific direction is transmitted through the first polarizer on the display screen side of the liquid crystal, and the other polarized light component is absorbed by this first polarizer. The direction of polarization of the light transmitted through the first polarizer is selectively varied in accordance with the orientation of the liquid crystal, which varies depending on the voltage applied to the liquid crystal, and the light impinges upon the second polarizer on the other side of the liquid crystal. For example, in a normally white mode, this external light behaves as follows with respect to each pixel: (i) when no voltage is applied to the liquid crystal, the light emitted from this liquid crystal is transmitted through the second polarizer and is further reflected by a reflection plate on the back side thereof, and then transmitted again through the second polarizer, the liquid crystal and the first polarizer to be emitted from the display screen of the liquid crystal display device as display light; and (ii) when a voltage is applied to the liquid crystal, the light emitted from this liquid crystal is absorbed by the second polarizer and no display light is eventually emitted from the display screen.
In this way, reflective type display is effected by controlling the quantity of display light emitted from the display screen for each pixel using the liquid crystal, polarizer or the like arranged in the optical path of external light while reflecting the external light impinging from the display surface by a reflection film provided inside the device.
In the case of the above mentioned transmissive type display, in the construction in which these two polarizers are provided, when light from a light source is emitted from behind the liquid crystal as seen from the display screen, only a polarized light component in a specific direction is transmitted through the second polarizer on the back side of the liquid crystal, and the other polarized light component is absorbed by this second polarizer. The direction of polarization of the light transmitted through the second polarizer is selectively varied in accordance with the orientation of the liquid crystal depending on the voltage applied to the liquid crystal, and the light impinges upon the first polarizer on the display screen side of the liquid crystal. This light from the light source behaves, for example, in normally white mode, as follows with respect to each pixel: (i) when no voltage is applied to the liquid crystal, the light emitted from this liquid crystal is transmitted through the first polarizer, and emitted from the display screen of the liquid crystal display device as display light, and (ii) when a voltage is applied to the liquid crystal, the light emitted from this liquid crystal is absorbed by the first polarizer and no display light is emitted from the display screen.
In this way, the transmissive type display is effected by controlling the quantity of light emitted from the display screen for each pixel using the liquid crystal, polarizer or the like arranged in the optical path of the light from the light source.
However, a polarizer, which is an example of the polarized light separator, effects polarization by absorbing the polarized light component which is in a direction different from a specific polarization axis direction of the incident light, so that the efficiency in the utilization of light is rather poor. Thus, in reflective type display and transmissive type display, which are effected, as described above, with two polarizers arranged on either side of the liquid crystal, the display is rather dark. If an attempt is made to brighten the display by simply replacing the polarizers by some other polarized light separation means, the contrast in display, which is regarded as important as the brightness of display, deteriorates.
The present invention has been made in view of the above problem. It is an object of the present invention to provide a display device of the type which can display high contrast and bright display at the reflective display and the transmissive display and an electronic apparatus using this display device in a display device utilizing a variable transmission polarization axis variable optical element such as liquid crystal.
The above object of the present invention is achieved by a display device comprising: variable transmission polarization axis means capable of varying a transmission polarization axis; first polarized light separating means which is arranged on one side of the variable transmission polarization axis means and which allows light that is a linear polarized light component in a first direction to be transmitted and reflects or absorbs light that is a linear polarized light component in a predetermined direction different from the first direction; second polarized light separating means which is arranged on the other side of the variable transmission polarization axis means and which allows light that is a linear polarized light component in a second direction to be transmitted and reflects light that is a linear polarized light component in a predetermined direction different from the second direction; a polarizer arranged on the opposite side of the variable transmission polarization axis means with respect to the second polarized light separating means; and a light source which is arranged on the opposite side of the second polarized light separating means with respect to the polarizer and which applies light to the variable transmission polarization axis means side, wherein the positional relationship between the second polarized light separating means and the polarizer is determined such that the second direction is deviated by a predetermined angle xcex8 (0xc2x0 less than xcex8 less than 90xc2x0) with respect to the direction of the transmission axis of the polarizer and deviated by a predetermined angle xcex8xe2x80x2 (0xc2x0 less than xcex8xe2x80x2 less than 90xc2x0) with respect to the direction of the absorption axis of the polarizer.
In the display device of the present invention, when reflective type display is effected by utilizing external light, external light is entered from the first polarized light separating means side. The first polarized light separating means allows the light of the linear polarized light component in the first direction of the incident external light to be transmitted to the variable transmission polarization axis means side. Then, the first polarized light separating means reflects or absorbs the linear polarized light component in the predetermined direction different from the first direction (for example, a direction orthogonal or substantially orthogonal to the first direction). Next, the second polarized light separating means allows the light of the linear polarized light component in the second direction of the incident light entering through the first polarized light separating means and the variable transmission polarization axis means to be transmitted to the side opposite to the variable transmission polarization axis means, and reflects the light of the linear polarized light component in the predetermined direction different from the second direction (for example, a direction orthogonal or substantially orthogonal to the second direction). As for the light transmitted through the second polarized light separating means, the component in the direction of the absorption axis thereof is absorbed by the polarizer, and, as for the light transmitted through the polarizer, it is reflected or diffused in the light source portion in a non-lighted state. On the other hand, the light reflected by the second polarized light separating means passes through the variable transmission polarization axis means and the first polarized light separating means in the reverse order as the above.
As a result, in the case of reflective type display, there are obtained a first (relatively bright) display state due to emission of the light reflected by the second polarized light separating means through the variable transmission polarization axis means from the first polarized light separating means side selectively in accordance with the direction of the transmission axis in the variable transmission polarization axis means, and a second (relatively dark) display state due to non-emission of the light transmitted through the second polarized light separating means from the first polarized light separating means side due to the absorption by the polarizer or the like. In particular, the positional relationship between the second polarized light separating means and the polarizer is determined such that the second direction is deviated by a predetermined angle xcex8 (0xc2x0 less than xcex8 less than 90xc2x0) with respect to the direction of the transmission axis of the polarizer, so that compared with the case in which the second direction coincides with the direction of the transmission axis of the polarizer (that is, xcex8=0xc2x0), the light transmitted through the second polarized light separating means is absorbed in a much larger quantity by the polarizer. Thus, by this quantity absorbed, the quantity of light emitted eventually from the first polarized light separating means in the above-described second display state can be reduced, whereby the contrast in the reflective type display can be enhanced. Regarding the brightness in the reflective type display, compared with the case in which a polarizer is used as the second polarized light separating means as in the conventional case (or in which polarizers are used for both the first and second polarized light separating means), polarized light separation is effected not by the absorption of light but by the reflection of light and this reflected linear polarized light component is utilized as the display light, whereby a bright reflective type display is obtained.
On the other hand, when transmissive type display is effected by utilizing a light source, light from the light source is incident on the second polarized light separating means through the polarizer. The second polarized light separating means causes light of the linear polarized light component in the second direction of the incident light from the light source to be transmitted to the variable transmission polarization axis means side, and reflects light of a linear polarized light component in a predetermined direction different from the second direction. Further, the first polarized light separating means causes the light of the linear polarized light component in the first direction of the light entering through the second polarized light separating means and the variable transmission polarization axis means to be transmitted to the side opposite to the variable transmission polarization axis means, that is, the display screen side. Then, it reflects the linear polarized light component in the predetermined direction different from the first direction.
As a result, in the case of transmissive type display, there are obtained, selectively in accordance with the direction of the transmission axis in the variable transmission polarization axis means, a third (relatively bright) display state due to emission of the light transmitted through the second polarized light separating means from the first polarized light separating means side, and a fourth (relatively dark) display state due to reflection of the light from the light source by the first polarized light separating means. In particular, the positional relationship between the second polarized light separating means and the polarizer is determined such that the second direction is deviated by a predetermined angle xcex8xe2x80x2(0xc2x0 less than xcex8xe2x80x2 less than 90xc2x0) with respect to the direction of the absorption axis of the polarizer, so that compared with the case in which the second direction coincides with the direction of the absorption axis of the polarizer (that is, xcex8xe2x80x2=0xc2x0), the light from the light source transmits in a much larger quantity through the polarizer and the second polarized light separating means. Thus, by this quantity transmitted, the quantity of light eventually emitted from the first polarized light separating means side in the above-described third display state can be increased, so that the contrast in the transmissive type display can be enhanced and, at the same time, the brightness can be enhanced.
In this way, by the display device of the present invention, it is possible to effect a high-contrast and bright display in a reflective type display and a transmissive type display and, in particular, it is possible to increase the brightness in a transmissive type display using light from a light source while enhancing the contrast in a reflective type display using external light.
In a form of the display device of the present invention, the first polarized light separating means consists of a reflective polarizer which allows the light of the linear polarized light component in the first direction to be transmitted and reflects the light of the linear polarized light component in a direction orthogonal to the first direction.
In this form, the reflective polarizer causes the linear polarized light component in the first direction of the incident light to be transmitted as the linear polarized light component in the first direction. Then, it reflects the linear polarized light component in the direction orthogonal to the first direction as the linear polarized light component in the orthogonal direction. Thus, display can be effected based on the light transmitted through the reflective polarizer.
In this form, the reflective polarizer may consist of a laminate formed by alternately stacking together birefringent first layers and second layers which have a refractive index that is substantially equal to one of the plurality of refractive indexes of the first layers and which are not birefringent.
In the reflective polarizer constructed as described above, the light of the linear polarized light component in the first direction of the incident light applied to one main surface of the reflective polarizer from the direction of lamination transmits to the other main surface on the opposite side as light of the linear polarized light component in the first direction. Then, the light of the linear polarized light component in the direction orthogonal to the first direction is reflected as the light of the linear polarized light component in the orthogonal direction. Of the light applied to the other main surface of the reflective polarizer from the direction of lamination, the light of the linear polarized light component in the first direction transmits to one main surface on the opposite side as the light of the linear polarized light component in the first direction. Then, the light of the linear polarized light component in the direction orthogonal to the first direction is reflected as the light of the linear polarized light component in the orthogonal direction.
In another form of the display device of the present invention, the first polarized light separating means consists of a polarizer which causes the light of the linear polarized light component in the first direction to be transmitted and absorbs the light of the linear polarized light component in the direction orthogonal to the first direction.
In this form, the polarizer causes the linear polarized light component in the first direction of the incident light to be transmitted as the linear polarized light component in the first direction and absorbs the linear polarized light component in the direction orthogonal to the first direction. Thus, display can be effected based on the light transmitted through the polarizer.
In another form of the display device of the present invention, the second polarized light separating means consists of a reflective polarizer which causes the light of the linear polarized light component in the second direction to be transmitted and reflects the light of the linear polarized light component in the direction orthogonal to the second direction.
In this form, the reflective polarizer causes the linear polarized light component in the second direction of the incident light to be transmitted as the linear polarized component in the second direction. Then, it reflects the linear polarized light component in the direction orthogonal to the second direction as the linear polarized light component in the orthogonal direction. Thus, display can be effected based on the light transmitted through the reflective polarizer.
In this form, the reflective polarizer may consist of a laminate formed by alternately stacking together birefringent first layers and second layers which have a refractive index that is substantially equal to one of the plurality of refractive indexes of the first layers and which are not birefringent.
In the reflective polarizer constructed as described above, the light of the linear polarized light component in the second direction of the incident light applied to one main surface of the reflective polarizer from the direction of lamination transmits to the other main surface on the opposite side as light of the linear polarized light component in the second direction. Then, the light of the linear polarized light component in the direction orthogonal to the second direction is reflected as the light of the linear polarized light component in the orthogonal direction. Of the light applied to the other main surface of the reflective polarizer from the direction of lamination, the light of the linear polarized light component in the second direction is transmitted to one main surface on the opposite side as the light of the linear polarized light component in the second direction. Then, the light of the linear polarized light component in the direction orthogonal to the second direction is reflected as the light of the linear polarized light component in the orthogonal direction.
In another form of the display device of the present invention, the second polarized light separating means causes the linear polarized light component in the second direction to be transmitted and reflects the light of the linear polarized light component in the direction orthogonal to the second direction with respect to the light of substantially the entire wavelength range of visible light. In this form, there are obtained, in reflective type display, two display states in accordance with the direction of the transmission polarization axis in the variable transmission polarization axis means with respect to external light of substantially the entire wavelength range of visible light range. In one of these display states, display due to transparent reflection or white reflection is obtained. on the other hand, when a white light source is used in transmissive type display, two display states are obtained in accordance with the direction of the transmission polarization axis in the variable transmission polarization axis means with respect to substantially the entire wavelength of visible light range, and, in one of these display states, display due to transparent reflection or white reflection is obtained.
In another form of the display device of the present invention, the transmission axis and the absorption axis of the polarizer are at right angles.
In this form, the polarizer is an existing polarizer in which the transmission axis and the absorption axis are at right angles, and the predetermined angle xcex8xe2x80x2=90 degreesxe2x80x94the predetermined angle xcex8. Thus, in both reflective type display and transmissive type display, satisfactory contrast and brightness can be obtained by using a relatively simple construction.
In another form of the display device of the present invention, the predetermined angle xcex8 is preferably 30 to 75 degrees.
In this form, more satisfactory contrast and brightness can be obtained in both reflective type display and transmissive type display.
In this form, more preferably, the predetermined angle xcex8 may be 45 to 60 degrees. In this construction, more satisfactory contrast and brightness can be obtained in both reflective type display and transmissive type display.
In another form of the display device of the present invention, the variable transmission polarization axis means consists of a liquid crystal element. That is, the display device may be formed as a liquid crystal display device.
Further, in this case, the variable transmission polarization axis means may be a TN liquid crystal element, an STN liquid crystal element or an ECB (Electrically Controlled Birefringence) liquid crystal element. In this construction, a bright, high-quality reflective type display can be effected relatively easily. The STN liquid crystal element includes an STN liquid crystal element using an optical anisotropic matter for color compensation. Further, when a liquid crystal element having a birefringent effect such as an ECB liquid crystal element, it is possible to vary the coloring from the light source.
In another form of the display device of the present invention, a second variable transmission polarization axis means is further provided on the opposite side of the variable transmission polarization axis means with respect to the second polarized light separating means.
In this form, in reflective type display, the second variable transmission polarization axis means adjusts the absorption of the external light transmitted through the second polarized light separating means, and the contrast can be adjusted. On the other hand, in transmissive type display, the second variable transmission polarization axis means adjusts the intensity of the light source light transmitted through the second polarized light separating means, and the brightness can be adjusted.
In this form, the second variable transmission polarization optical axis means may consist of a liquid crystal element.
Further, in this case, the second variable transmission polarization axis means may be a TN liquid crystal element, an STN liquid crystal element or an ECB (Electrically Controlled Birefringence) liquid crystal element.
Further, in this form equipped with the second variable transmission polarization axis means, the second variable transmission polarization axis means may be arranged between the second polarized light separating means and the polarizer.
In this construction, for reflective type display, the direction of the linear polarized light transmitted through the second polarized light separating means is varied with respect to the transmission axis of the polarizer by the second variable transmission polarization axis means, whereby the proportion of the linear polarized light absorbed by the polarizer can be arbitrarily adjusted. Further, for transmissive type display, the direction of the linear polarized light transmitted through the polarizer is varied with respect to the second direction of the second polarized light separating means by the second variable transmission polarization axis means, whereby the proportion of the linear polarized light transmitted through the second polarized light separating means can be arbitrarily adjusted. As a result, the adjustment of contrast in reflective type display and the adjustment of brightness in transmissive type display can be conducted.
In another form of the display device of the present invention, a light transmitting light-diffusing means is further provided between the light source and the first polarized light separating means.
In this form, it is possible to effect a (paper-like) display that is not in a mirror finished surface state by the light transmitted through the first polarized light separating means and output as display light. The light-diffusing means may be arranged, for example, between the first polarized light separating means and the variable transmission polarization axis means or between the variable transmission polarization axis means and the first polarized light separating means.
The above object of the present invention can also be achieved by an electronic apparatus equipped with a display device according to the present invention as described above.
Since the electronic apparatus of the present invention is equipped with the above-described display device of the present invention, it is possible to realize various electronic apparatuses in which it is possible to effect bright display while maintaining the contrast at a desired level. Depending on its use, the electronic apparatus of the present invention may be equipped with one of the various forms of display device described above.
The object of the present invention can also be achieved by a display device comprising: a variable transmission polarization axis optical element; a first polarized light separator which is arranged on one side of the variable transmission polarization axis optical element and which effects polarized light separation by reflection or absorption; a second polarized light separator which is arranged on the other side of the variable transmission polarization axis optical element and which effects polarized light separation by reflection; a polarizer arranged on the opposite side of the variable transmission polarization axis optical element with respect to the second polarized light separator; and a light source which is arranged on the opposite side of the second polarized light separator with respect to the polarizer and which applies light to the variable transmission polarization axis optical element side, wherein the positional relationship between the second polarized light separator and the polarizer is determined such that the second direction is deviated by a predetermined angle xcex8 (0xc2x0 less than xcex8 less than 90xc2x0) with respect to the direction of the transmission axis of the polarizer and deviated by a predetermined angle xcex8xe2x80x2 (0xc2x0 less than xcex8xe2x80x2 less than 90xc2x0) with respect to the direction of the absorption axis of the polarizer.
As described above, in this display device, it is possible to obtain a high-contrast and bright display.
In the above-described display device of the present invention, it is possible to realize a bright reflective type display if it is formed as a display device of any well-known driving system such as the simple matrix system, the active matrix system using TFT (Thin Film Transistor), TFD (Thin Film Diode) or the like, or the segment system.
Further, apart from the above-described reflective polarizer, the polarized light separating means of the present invention may, for example, be a polarized light separating means consisting of a combination of a cholesteric liquid crystal layer and a (xc2xc) xcex plate, a polarized light separating means which effects separation into reflective polarization and transmissive polarization by utilizing Brewster""s angle (See pp. 427-429 of S1D 92 D1 GEST), a polarized light separating means utilizing hologram, polarized light separating means disclosed in an internationally laid-open international application (Internal Publications No. WO95/27819 and WO95/17692) or the like. In each of the embodiments described below also, these polarized light separators can replace the reflective polarizer.